Airborne Ti dropbar mtb, Self built 650c frame/fork, Guerciotti SL, Schwinn Circuit SS, Intense BMX Cruiser, 1966 Bianchi Folding bike
I'd say mid to maybe early 70's . The bottle mount and nutted brake bridge pushes it in that time frame for me. When did bottle mounts first start showing over the clamp on style on frames? I don't recall seeing many frames from the 60's with bolt on bottle cages and have even seen Colnagos from the 70's using a clamp on cage.
I agree that the stay caps are "Gios-like" but not exactly the same, for one thing the stays are single-taper so larger at the top than is typical for most Gios I have seen.
Another not-so-great clue for you: Olmo used the same head lugs in the '80s but not with that heart-shaped cut-out (They would have had a star if any).